1. Technical Field of the Invention
The present invention relates in general to the mobile radio communications field and, in particular, to a method and system for use in determining the geographical position of a mobile radio terminal.
2. Description of Related Art
Commonly-assigned U.S. patent application Ser. No. 08/917,577 to Hagerman et al., describes a method for determining the position of a mobile radio terminal (hereinafter mobile station or MS), which makes use of uplink Time of Arrival (TOA) and Direction of Arrival (DOA) measurements. Slight mention is made in that disclosure about repeating the same uplink signal a number of times, in order to improve the accuracy of the TOA determinations. However, the disclosure does not provide any details about how this improvement can be achieved.
Commonly-assigned U.S. Patent Application Serial No. (Attorney docket no. 27946-00353), which has been filed on the same day as the present application, discloses a method and apparatus for providing a "prime" uplink signal from a MS whose position is to be determined. The present invention is related by subject matter to the above-described Patent Applications and teaches how to process a repeated uplink signal, such as, for example, the "prime" uplink signal from a MS whose position is to be determined.
The CME 20 System, which is a Global System for Mobile Communications (GSM) implementation manufactured by Telefonaktiebolaget LM Ericsson, sends uplink messages with a Timing Advance (TA) to compensate for the radio signal propagation delay caused by the distance between the radio base station (BS) and the MS. The TA value is determined by a procedure of selecting the smallest TA value from a number of measurements made by the BS on several access bursts that have been transmitted by the MS. For TA value determinations, this procedure solves the radio signal multipath propagation problem (i.e., when the signal propagates along a line of sight path and also along one or more reflected paths). This procedure is hereinafter referred to as the "minimum time" method.